The present invention relates to systems and methods of injecting a patient (human or animal) with both an object and an amount of fluid. There are many applications where it is desired that an object, such as a radio transponder, a collagen pellet, a caplet of medicine, etc., be delivered into the tissue of a patient at a particular location along with an amount of fluid. For example, such co-injection procedures may be performed to deliver pet identification microchips with a vaccine or anti-body. Some approaches to such procedures are described in Teoh U.S. Pat. No. 5,288,291 and Taylor et al. U.S. Pat. No. 5,211,129. The present invention, however, sets forth improvements on the systems and methods for co-injection.